UI hangs after "Sign In" canceled by user

[Jin]

Description:
Telegram's UI is broken after user canceled the "Sign In" process.

Reproduce Steps:
    a) Launch Telegram
    b) Enter the country code and phone number
    c) To enter the page "Sign In" to input the authentication code
    d) Press back key/arrow to return to previous page
    e) Observe the Telegram UI

Expected Result:
User can return back to previous page (input phone number),
and the further authentication process could be completed successfully.

Actual Result:
UI hangs and the timer stops.

Occurrence:
10/10 (100%)

Software Information:
    com.ubuntu.telegram (2.2.26.0)

Hardware Information:
    current build number: 480
    device name: mako
    channel: ubuntu-touch/rc-proposed/ubuntu
    last update: 2016-07-07 11:36:27
    version version: 480
    version ubuntu: 20160706.1
    version device: 20160401.1
    version custom: 20160706.1